This invention relates to fluid-flow devices wherein the quantity of fluid that flows through a nozzle is being regulated by variations of the nozzle gap, i.e. the gap formed between the valve stem and the valve seat. To be more specific, valves according to this invention are more particularly applicable wherever it is desired to provide pneumatic insulation between a fluid stream impinging upon a measuring diaphragm, particularly a rolling diaphragm, and a valve stem cooperating with a valve seat under the action of said diaphragm, or rolling diaphragm. The above referred-to operation of the valve is free floating and is obtained by a perforated flexible or resilient baffle plate through which the valve stem projects, and a contiguous "O"ring closely surrounding the valve stem. This arrangement combines high pneumatic stability with low valve stem friction.
This invention relates more particularly to so-called pneumatic reversing relays though it is not limited to this kind of valves as will be more apparent from the following description of the invention. The embodiment shown in FIG. 1 of the drawings shows a 1:1 reversing relay wherein the output of the relay is a regulated pressure, the magnitude of which depends on the initial pressure and the magnitude of the signal pressure according to the relationship EQU Pout=Pset-P signal (1)
wherein
Pout=output pressure; PA1 Pset=the set pressure (determined by spring action); and PA1 Psignal=the signal pressure.
Assuming a pneumatic reversing relay is provided with three diaphragms, or three rolling diaphragms, as shown below in greater detail, then the ratios between the effective area of the diaphragms may change, e.g. 1:2; 2:1; 1:3; 3:1; etc. Referring to the effective areas of a three diaphragm pneumatic reversing relay as A.sub.1, A.sub.2 and A.sub.3, then EQU K=(A.sub.1 -A.sub.2)/A.sub.3 ( 2)
Combining equations (1) and (2) yields EQU Pout=Pset-K.multidot.Psignal
This equation can be converted to direct rather than reverse acting and would then read EQU Pout=Pset+K.multidot.Psignal.
The above relationships apply both to pneumatic prior art relays and to relays according to the present invention, but the means for complying with them are very different in both instances.
A feature of the present invention consists in that the top portion of the above referred-to valve stem is larger, i.e. has a larger diameter, than the supply seat diameter of a supply valve whose valve element, or pintle, is supported by the same valve stem. A compression spring is arranged between the large diameter portion of the valve-stem of the regulating valve and the valve seat of the supply valve, tending to close both valves. The above valve stem is supported by an "O"ring and the supply valve. This has the advantage of allowing the passageway formed by the relatively narrow lower portion of the valve stem to be used for the admission of supply air and to dispense with a special support for the lower end of the aforementioned valve stem biasing compression spring. This feature and its advantages will become more apparent as this specification proceeds.
The valve element, or pintle, of the supply valve has a novel shape, i.e. its upper end that cooperates with the valve seat is spherical, and its lower end remote from the valve seat is conical, or in the shape of a frustum of a cone. The object of the spherical portion is to establish good contact with the valve seat in the event of angular tilting, and the object of the conical portion is to prevent excessive indentation in the valve seat and to make the part easier to machine and handle during assembly. Prevention of indentation is an important feature since the valve seat consists of a material that can easily be permanently deformed such as, for instance, a plastic, such as an acetal plastic.
The invention further comprises a novel way of attaching the valve seat of the supply valve to the other parts of the valve structure which excels on account of its ruggedness against shock, vibrations and temperature variations, as well as its compactness and low production cost. This aspect of the invention will be described below in greater detail.
As is apparent from the above, pneumatic relays according to this invention include a plurality of diaphragms, or rolling diaphragms. These include a radially inner or central clamping portion or flange, a radially outer annular clamping portion or flange, and an intermediate rolling wall. The diaphragm flanges of prior art rolling diaphragms are subject to pull-out, creep and relaxation of the clamping forces. According to this invention a low compression material such as a felt of random oriented dacron fibers is molded in one or both diaphragm flanges which cooperate with clamping means, or hardware, having a system of concentric circular grooves mating with clamping flange, or flanges, of the rolling diaphragm. When pressure is applied to the clamping flanges of the rolling diaphragm, some of the rubber content thereof is forced into the aforementioned grooves which greatly increases the pull-out resistance of the diaphragm. The low compression material in the flange, or flanges, of the rolling diaphragm reduce the creep and relaxation of the clamping forces.
It will be apparent from the above that the objects of this invention include an improvement of pneumatic relays, in particular pneumatic reversing relays, and an improvement of the constituent parts thereof. The improvements are particularly concerned with the main nozzle structure and its associated parts, the supply nozzle structure and its associated parts and the rolling diaphragms of the structure. Other inventive improvements will become fully apparent as this specification proceeds and will be pointed out in the appended claims.